This proposed investigation would continue into adulthood a longitudinal study of 38 individuals with sex chromosome abnormalities (SCA) who have been followed since birth. Identified through the chromosome screening of 40,000 consecutive newborns, this cohort is free of the selection bias characteristics of clinically identified propositi. Controls will include 25 siblings of the propositi. All subjects will be seen annually over a period of four years. The long-term objective of this project has been to establish the phenotype and developmental prognosis of SCA children, adolescents, and adults. Building upon previous findings associated with learning, motor, language, behavioral, and endocrine problems, this protocol targets four assessment areas: 1) Brain structure, which the pilot data indicate is altered by SCA; 2) Language abilities, specifically verbal fluency, phonologic awareness, reading, and auditory short-term memory, believed to be influenced by SCA; 3) Psychosocial adaptation, diminished in many SCA adolescents; and 4) Physical and endocrine problems, seen in some propositi and possibly becoming more prevalent in adulthood. Retrospective evaluation of family relationships is planned to determine sources of resilience in propositi with normal development and strong adaptation. Results from this long-range project have already been used both in genetic counseling of parents of a prenatally diagnosed SCA fetus, and to provide guidance to SCA parents and their families. No similar data on SCA adult adaptation are available, and this is one of only two studies in the world continuing to follow an unselected cohort of SCA propositi. It is unlikely that any such study will be initiated again in the foreseeable future.